The present invention relates to a temperature detecting device. More particularly, the invention relates to a temperature detecting device for use in electronic fire alarm systems having a heat detecting section provided with a heat collector in which a semiconductor element is employed as a heat detecting element.
In general, it is well-known in the art that a forward voltage drop developed across the P-N junction of a semiconductor diode will vary linearly over a wide range of temperature when the forward current thereof is held constant. Hence, semiconductor diodes have widely been used as heat detecting elements because of their stable and reliable characteristics. Since it is necessary to both detect the variations in temperature and then amplify the derived signal representing variations, it has been proposed that the P-N junction of a transistor be used as a semiconductor diode.
FIG. 1 is a schematic diagram including a cut-away portion which shows an example of a conventional temperature detecting device in which a transistor is employed as a heat detecting element. The conventional temperature detecting device includes, as shown in FIG. 1, a casing 1 housing a reference voltage generating circuit, a comparator circuit, a switching circuit and the like, and a metal protective tube 2 having a high heat conductivity mounted on the casing 1. So as to improve the heat response characteristics, a metal case hermetically sealed transistor 5 is provided at the top portion in the inner housing of the metal tube 2 held in place by an insulating adhesive agent.
More specifically, the metal hermetically sealed transistor is provided with three lead lines one of which is electrically connected to a metal case of the transistor 5 and an insulating material 11 such as alumina or the like is provided between the transistor 5 and the metal protective tube 2 so that they are electrically insulated. To provide the electrical insulation, a metal tube having a large inner diameter must be employed as the metal protective tube 2. This results in increasing the heat capacity of the metal protective tube 2 because of the presence of the insulating material 11. Furthermore, with the above described construction, the transistor pellet itself within the metal case is far from the metal protective tube 2 and, accordingly, the heat response characteristics are degraded.
Accordingly, the conventional temperature detecting device has a disadvantage in the lack of heat response characteristics. Therefore, the above-mentioned conventional temperature detecting device cannot be employed as a heat detecting section of a fire alarm system which must detect unusually rapid increases in ambient temperature.
In order to further improve the heat response characteristics of the heat detecting section, it has been proposed that a heat collector be provided for the heat detecting section of the temperature detecting device. With respect to the technique used for mounting the heat collector to the heat detecting section of the temperature detecting device employing a bimetallic device or a semiconductor as a heat detecting element, as disclosed in Unexamined Published Japanese Utility Model Application Nos. 25490/1975 and 98090/1976, the heat collector may be stacked on the heat detecting section or, as set forth in Unexamined Published Japanese Utility Model Application No. 130691/1977, the heat collector may be secured to the heat detecting section by spot welding or it may be secured to the heating detecting section by an adhesive agent. However, these conventional techniques require a large number of manufacturing steps as a result of which manufacturing costs are high so that such techniques are not economical. In addition, as the heat collector is secured by the use of an adhesive agent, endothermic action of the adhesive agent results in a decrease of the heat collecting effect of the heat collector.